1. Field of Invention
The invention relates to fuel injection systems and methods.
2. Description of Related Art
Japanese Laid-Open Patent Application No. 2000-265877 discloses a fuel injection system which includes a fuel injection valve that injects fuel into an intake passage of an internal combustion engine (to be referred to as an “intake passage injection valve”), and another fuel injection valve that injects fuel into a combustion chamber of the engine (to be referred to as an “in-cylinder injection valve”). In operation, this fuel injection system injects fuel using both the valves during an engine start operation in order to prevent an engine start failure, i.e., to ensure a good engine startability.
Meanwhile, Japanese Laid-Open Patent Application No 2000-179368 discloses another fuel injection system which includes a fuel injection valve that injects fuel into an intake port of an internal combustion engine (to be referred to as an “intake port injection valve”), and an in-cylinder injection valve such as aforementioned. The intake port injection valve supplies high octane fuel while the in-cylinder injection valve supplies low octane fuel, and fuel is injected using the intake port injection valve only, or using both of the injection valves, depending upon the engine load. Namely, by selecting the injection valve(s) to be used, the octane rating of fuel in an air-fuel mixture in a combustion engine is changed in accordance with the engine load in order to prevent knocking of the engine.
In the field of internal combustion engines, in addition to ensuring a sufficient engine startability, it is earnestly desired to reduce the emission of smoke. As is known, inadequate combustion of fuel results in generation of smoke in the combustion chamber, and it is therefore important to reduce the amount of such smoke as much as possible.